This research project is a continuation of a previous project in which a procedure was developed for constructing a physical map of genes. This procedure involves electron microscopic visualization of ribosome binding sites (translational start sites). Ribosomes are bound to single-stranded DNA, fixed with glutaraldehyde, and the position along the DNA measured. A map constructed for the early and immunity regions of lambda DNA agreed closely with the map determined by other procedures. This map has now been extended to cover the entire half of lambda DNA including the nin5 region. Further proposed experiments include: 1) mapping of other bacterial virus and plasmid DNA, 2) determining if the binding affinity for different binding sites is correlated with the amount of polypeptide product synthesized in vivo, 3) studying translational control in phage phi X174.